Method and apparatus for testing mobile terminals in an OFDM system

ABSTRACT

The present invention relates to a method and apparatus for testing mobile terminals in an OFDMA system, in which all or part of available downlink radio resources in a cell are transmitted. A processing unit in a test apparatus splits the resources used for transmission into contiguous unities in the frequency domain such that one or more of said unities comprise resources allocated to one or more mobile terminals under test, and at least one of said unities comprise resources allocated to virtual users.

RELATED APPLICATIONS

This application claims priority to International Application No.PCT/SE2008/051421 filed on Dec. 8, 2008, and to U.S. ProvisionalApplication No. 61/061,290 filed on Jun. 13, 2008, the contents both ofwhich are incorporated herein by reference in their entirety.

BACKGROUND

Different types of User Equipment, UE, performance requirements arespecified in the standard. In order to ensure that UE meets theserequirements, appropriate and relevant test cases are also specified.During the tests all the downlink radio resources are not typicallyneeded for the user under test. In practical circumstances several usersreceive transmission simultaneously on different resources in a cell. Tomake the tests as realistic as possible these remaining channels orradio resources should be transmitted in a manner that mimicstransmission to other users in a cell.

The objective of UE performance verification (or the so-called UEperformance tests) is to verify that UE fulfils the desired performancerequirements in a given scenario, conditions and channel environment. Bydesired performance requirements it is meant those specified in thestandard or requested by an operator or by any prospective customer. Theperformance requirements span a very vast area of UE requirements, suchas:

-   -   UE RF receiver requirements e.g. receiver sensitivity    -   UE RF transmitter requirements e.g. UE transmit power accuracy    -   UE demodulation requirements e.g. achievable throughput    -   Radio resource management requirements e.g. handover delay        We can classify the UE verification into two categories:    -   Verification in lab    -   Verification in real network        Verification in Lab

In the verification in lab the base station is emulated by testequipment, which is often termed as system simulator. Thus all downlinktransmission is done by the test equipment to the test UE. During a testall common and other necessary UE specific control channels aretransmitted by the test equipment. In addition a data channel, e.g.PDSCH in E-UTRAN, is also needed to send necessary data and configurethe UE. Furthermore typically a single UE is tested at a time. In mosttypical test cases the entire available downlink resources are not usedby the UE. However to make test realistic the remaining downlinkresources should also be transmitted to one or multiple virtual users.

In OFDMA system the transmission resources comprises of time-frequencyresources called resource blocks, which are sent with some transmitpower level, as described in more detail below. This type of resourceallocation to generate load in OFDMA will be referred to as OFDM channelnoise generator (OCNG) in the following. Thus OCNG is sent to aplurality of virtual users for loading the cell.

Verification in Real Network

These types of tests are demanded by the operators and are performed ina real network. The test may comprise of single or multiple UEs. Priorto the network roll out or in an early phase of deployment the trafficload is typically very low. In classical tests the cell load isgenerated by increasing transmission power on one or more commonchannels. However operators are now increasingly demanding the networkvendors to generate cell load in realistic fashion for performing tests.This means resources, which are not allocated to the test users shouldbe allocated to the virtual users emulating load in the cell. Thuseither all or large part of available resources i.e. channels, transmitpower etc is used in the tests. This requires base station to implementthe ability to transmit remaining resources in order to generate load.Thus for OFDMA (i.e. in E-UTRAN) OCNG is also deemed to be implementedin an actual base station.

Noise Generation in WCDMA for UE Performance Verification

In WCDMA orthogonal channel noise simulator (OCNS) is used to load cellsin the test. The OCNS is implemented in both test equipment and alsopossibly in the base station. In the former case it is standardized inTS 25.101 and TS 25.133 for each type of test or same for similar tests.The OCNS comprises of channelization code and relative power. In a CDMAsystem the position of channelization code in a code tree is sensitiveto intra-cell interference. Therefore more careful selection of codesfor OCNS and their power levels is needed. An example of OCNS from TS25.101 for UE demodulation tests is quoted below:

TABLE 1 DPCH Channelization Code and relative level settings for OCNSsignal Relative Level Channelization setting (dB) (Note Code at SF =128 1) DPCH Data (see NOTE 3) 2 −1 The DPCH data for each 11 −3channelization code shall be 17 −3 uncorrelated with each other and 23−5 with any wanted signal over the 31 −2 period of any measurement. For38 −4 OCNS with transmit diversity the 47 −8 DPCH data sent to eachantenna 55 −7 shall be either STTD encoded or 62 −4 generated fromuncorrelated 69 −6 sources. 78 −5 85 −9 94 −10 125 −8 113 −6 119 0 NOTE1: The relative level setting specified in dB refers only to therelationship between the OCNS channels. The level of the OCNS channelsrelative to the Ior of the complete signal is a function of the power ofthe other channels in the signal with the intention that the power ofthe group of OCNS channels is used to make the total signal add up to 1.NOTE 2: The DPCH Channelization Codes and relative level settings arechosen to simulate a signal with realistic Peak to Average Ratio. NOTE3: For MBSFN, the group of OCNS channels represent orthogonal S-CCPCHchannels instead of DPCH. Transmit diversity is not applicable to MBSFNwhich excludes STTD.E-UTRAN Downlink Transmission

In E-UTRAN Orthogonal Frequency Division Multiplexing (OFDM) technologyis used in the downlink, whereas DFT based pre-coded OFDM is used inuplink. In E-UTRAN the cell transmission bandwidth is divided intoseveral time-frequency resources. Most of these resources comprise ofresource blocks, which comprises of 0.5 ms (time slot) in time domainand 12 sub-carriers each of 15 kHz in frequency domain. However some ofthe resources used for common channels e.g. SCH channel (primary andsynchronization sequences) or reference symbols are transmitted over oneor more OFDM symbol in time domain in each sub-frame. Some other controlsignals such as PCFICH, PHICH and PDCCH are also sent in specific OFDMAsymbol in each sub-frame. The resource blocks are used for transmitteduser data or some control signaling e.g. paging, system information etc.

Furthermore E-UTRAN is a pure packet data designed cellular system, inwhich transmissions of user data in uplink and downlink always takeplace via shared channels. As similar to HSPA in UTRAN, the UE monitorsphysical downlink control channels (PDCCH) in order to access UEdedicated user data on the physical downlink shared channel (PDSCH) andthe network assigns uplink scheduling grants to the UE on demand basisfor uplink transmission via the physical uplink control channel (PUCCH)and the physical uplink shared channel (PUSCH). Error detection isprovided on transport blocks and control payloads through CyclicRedundancy Check (CRC) on PDSCH and PUSCH, and HARQ operations ensureefficient re-transmissions.

In E-UTRAN, no downlink transmit power control (TPC) has been specifiedand uplink TPC commands are embedded in the control payload mapped toPDCCH, which are sent occasionally or frequently by the E-UTRAN basestation (eNodeB).

Downlink Physical Signals and Channels in E-UTRAN.

The physical layer signals and channels in E-UTRAN downlink are:

-   -   Physical layer signals, i.e. reference signal (pilots) and        synchronization signals;    -   Physical broadcast channel (PBCH);    -   PDCCH and PDSCH;    -   Physical control format indicator channel (PCFICH); and    -   Physical HARQ indicator channel (PHICH)

Following observations can be made:

-   -   Physical layer signals and PBCH are transmitted periodically;    -   Error detection via CRC of transport blocks mapped to PBCH and        PDSCH, and of control data mapped to PDCCH;    -   Some uplink transmissions shall result in downlink responses        through the physical channels PDCCH and PHICH.

The cell load is generated by OCNS in WCDMA, UTRAN TDD or other CDMAsystems. The same concept is not needed in E-UTRAN since radio interfaceis based on OFDMA technology, which is less sensitive to intra-cellinterference. But there is still some leakage across the sub-carrierscontributing to intra-cell interference due to transmitter and receiverimperfections. However inter-cell interference is not orthogonal andtherefore it can still be considerable in OFDMA like in CDMA. Currentlyno rules on how to generate cell load for performing UE performance testare available for OFDMA systems.

SUMMARY

Thus, the objective of this invention is to define rules for loading thecell or test equipment based on OFDMA technology in the downlink forperforming UE tests in realistic manner and according to well definedprinciples.

A first aspect of the present invention relates to a method forperforming tests of mobile terminals or UEs designed to operate in anOFDMA system. During the test, all or part of available downlink radioresources in a cell of the OFDMA system are transmitted. One exemplarymethod comprises splitting said radio resources used for transmissioninto contiguous unities in the frequency domain such that one or more ofsaid unities comprise radio resources allocated to one or more mobileterminals under test and at least one of said unities comprise radioresources allocated to virtual users. The method may further includetransmitting test signals to the mobile terminals under test on theresources allocated to the mobile

Since the mobile terminals under test only decode mobile terminalspecific channels, and not the channels used for the virtual users, thesplitting of the transmitted resources means that the decoding is madeless complex. Thus, the method according to this aspect of theinvention, involving separating the resources allocated for the mobileterminals under test and for the virtual users respectively intoseparate unities in the frequency domain, provides consistency to thetest performance by applying the specified rule that implies a lowcomplexity and constrain on the mobile terminals performing the test.

Here, the term “contiguous” has the meaning of a consecutive, i.econtinuous, arrangement within each unity.

In a specific embodiment of the invention, the resources are split suchthat one or more contiguous unities of resources in the center of anavailable cell bandwidth are allocated to the one or more mobileterminals under test, and one or more contiguous unities of resources atthe edges of said cell bandwidth are allocated to virtual users.

In another specific embodiment, the resources are split such that one ormore contiguous unities of resources at the edges of said cell bandwidthare allocated to the one or more mobile terminals under test, and one ormore contiguous unities of resources in the center of an available cellbandwidth are allocated to virtual users.

A second aspect of the invention relates to test apparatus for testingmobile terminals designed to operate in an OFDMA system. During testing,all or part of available downlink radio resources available in a cell ofthe OFDMA system are transmitted. In one exemplary embodiment, the testapparatus comprises a processing unit configured to split said radioresources into contiguous unities in the frequency domain such that oneor more of said unities consists of resources allocated to the one ormore UE under test and at least one of said unities consists ofresources allocated to virtual users. The test apparatus may furtherinclude a transmitter operatively connected to the processing unit fortransmitting test signals to said one or more mobile terminals onresources allocated to the mobile terminals and to the virtual users onradio resources allocated to said virtual users.

Rules governing virtual users to load cells could be specified in thestandard for all tests and should be implemented in the test equipment.They may also be implemented in actual base stations for verifyingoperator specific or standardized tests in real network.

Thus, the test apparatus according to said second aspect of theinvention may e.g. be an OFDM simulator for simulating an OFDM system ora radio base station capable of operating in an OFDM system, such as aneNodeB (Evolved NodeB).

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following detailed description ofpreferred embodiments as illustrated in the drawings.

FIG. 1 illustrates an exemplary allocation of radio resources whereinresources at edges of cell transmission bandwidth are allocated tovirtual users;

FIG. 2 illustrates an exemplary allocation of radio resources whereinradio resources in the center of cell transmission bandwidth areallocated to virtual users;

FIG. 3 illustrates a method according to a first embodiment of theinvention;

FIG. 4 illustrates a method according to a second embodiment of theinvention;

FIG. 5 illustrates a method according to a third embodiment of theinvention;

FIG. 6 illustrates a test apparatus capable of carrying out embodimentsof the invention.

DETAILED DESCRIPTION

The present invention can be exemplified in the following non-limitingdescription of embodiments of the invention.

Typically only a single mobile terminal, also known as a user equipment(UE) is tested at a time in a lab to verify that the UE under test meetsthe performance requirements. When test is performed in real networkthere can be one or multiple UE but in any case the entire cellresources are rarely used. Thus both in a lab or real network tests, theunused resources are transmitted to non existing virtual UEs to load thecell and to thereby mimic a realistic scenario seen in an actualnetwork. The objective of this invention is to define rules, which canbe used to transmit both test UE(s) and virtual UEs when verifying UEperformance requirements in an OFDMA system. In order words, rulesshould define the split of OFDMA cell transmission resources between thetest user(s) and the virtual users, also referred to as OFDM channelnoise generator (OCNG) users. According to embodiments of the invention,resources allocated to the UE or UEs under test and the virtual usersare split into contiguous unities. The UE (or UEs) under test does notdecode OCNG channels, but only has to decode UE specific channels suchas PDSCH and other UE specific channels, for example paging mapped onPDSCH. The objective of OCNG, i.e. virtual users, is only to load thecell in order to create realistic test environment, and not to addcomplexity to the decoding of UE specific channels e.g PDSCH. Suchunnecessary complexity would put additional constraint on the UE that isnot relevant for the test performance itself. For the test performance,it is desirable to isolate the test environment from influence that isnot relevant for the test. Unnecessary complexity could cause suchproblems for the UE under test that the purpose of the test being lost,and thus the test would be of no use. Furthermore, randomly generated ordistributed arrangement of resources allocated to the UE under testcould also lead to inconsistent test results.

FIG. 3 illustrates a method according to an embodiment of the invention,performed by a transmitting unit for example a base station or a systemsimulator. The test performance is started in step 301. In step 302, theresources to be transmitted in the test are split in the frequencydomain such that certain contiguous unit or units is/are allocated tothe UE or UEs under test, and certain other contiguous unit or unitsis/are allocated to virtual users, also referred to as OCNG users. Thetransmitting unit thereafter transmits according to said split, step303.

The embodiments described in the following apply to verification testsin lab as well as those done in a real network.

According to an embodiment of the invention, all the available cellresources (i.e. in test equipment that mimics base station or an actualbase station in case of real network test) are divided into three maingroups: X, Y and Z. They are allocated as follows:

-   -   Group X resources are allocated to common channels, whose        position in time and frequency domains are well specified.        Examples of common channels are: SCH, PBCH, reference symbols,        PCFICH, PDCCH etc    -   Group Y resources are allocated to the test user(s).    -   Group Z resources are indeed OCNG and are allocated to virtual        users, also called OCNG users.

Since common channel allocation is already well defined in the standard,the embodiments described herein will focus on how cell resources aresplit between group Y, i.e. resources allocated to the test users, andgroup Z, i.e. resources allocated to OCNG users.

In radio resource management (RRM) tests such as tests related tohandover or cell reselection, typically two or more cells are used,where for instance one of the cells is a target cell. Group Y, i.e. theresources allocated to the test users, is in that case used forconfiguring UE via the initial or a serving cell. This means that as aspecial case the Y group can be zero in one or more of the cellsinvolved in some RRM tests.

According to one specific embodiment, the resources are allocated suchthat OCNG users are allocated resource blocks at the edges of the cellbandwidth, while the test user(s) is/are allocated resource blocks (i.e.group Y) in the middle of the cell transmission bandwidth in contiguousmanner. Typically, the common channels such as SCH, PBCH, referencesymbols, PCFICH, PDCCH are also located in the center of the bandwidth.Thus, the resource blocks allocated to the virtual users i.e. group Z,are arranged in contiguous unities in frequency domain at the edges ofthe cell bandwidth and scheduled and transmitted to OCNG users, i.e.virtual users. This arrangement is shown in FIG. 1. A method accordingto this embodiment, performed by a transmitting unit, for example a basestation or a system simulator, is illustrated in FIG. 4. The testperformance is started in step 401. In step 402, the resources to betransmitted in the test are split in the frequency domain such that acontiguous unit of resource blocks in the center of the cell bandwidthis allocated to the UE or UEs under test, while a contiguous unit ofresource blocks at each edge of the cell bandwidth is allocated tovirtual users, also referred to as OCNG users. The transmitting unitthereafter transmits according to said split of resources, step 403.

According to an alternative specific embodiment, the resources areallocated such that OCNG users are allocated resource blocks in themiddle of the cell bandwidth, while the test user(s) is/are allocatedresource blocks (i.e. group Y) at one or both edges of the celltransmission bandwidth in contiguous manner. Thus, the resource blocksallocated to virtual users, i.e. group Z, are arranged in contiguousunities in frequency domain in the center of the cell bandwidth and aretransmitted to OCNG users, i.e. virtual users when carrying out thetest. This arrangement where OCNG is transmitted in center of thebandwidth is shown in FIG. 2. A method according to this embodiment,performed by a transmitting unit for example a base station or a systemsimulator, is illustrated in FIG. 5. The test performance is started instep 501. In step 502, the resources to be transmitted in the test aresplit in the frequency domain such that a contiguous unit of resourceblocks at each edge of the cell bandwidth is allocated to the UE or UEsunder test, while a contiguous unit of resource blocks in the center ofthe cell bandwidth is allocated to virtual users, also referred to asOCNG users. The transmitting unit thereafter transmits according to saidsplit of resources, step 503.

The allocation of resource blocks between the test users and the virtualusers may be fixed, for example such that 50% of all available resourceblocks are allocated to the test user(s). For instance in case of 10 MHzbandwidth there are in total 50 RB, out of which 25 RB can be allocatedto test user(s). In lab test there is typically only one user andtherefore all 25 RB would be assigned to this user. In case of two ormore test users the resource blocks can be equally split between theusers or split with different proportion depending upon the type ofinformation to be sent to these users. Dummy data may be transmitted incase the resources allocated to the UE under test are redundant for thetest user. This will keep the number of resource blocks constant ingroup Y and make the test case more stable. The dummy data may compriseof some random sequences, which are stored in the test equipment andperiodically sent to the virtual OCNG users.

In a specific arrangement there will be one resource block assigned pereach individual OCNG user i.e. there will be as many OCNG users as thenumber of resource blocks in group Z. In the example above (10 MHzbandwidth) there should according to this rule be 25 OCNG users (i.e. 1RB per OCNG user). A low bit rate data (e.g. voice service) can betransmitted to OCNG users. In another arrangement there can be fewerOCNG users than the number of resource blocks in group Z, whereby morethan one resource block are allocated to each OCNG user. For instance inthe above example, if we have five OCNG users, then five resource blocksare allocated to each OCNG user.

It should be noted that in specific embodiments, power can be differenton different resource blocks due to power boosting on some channels toimprove coverage. This may depend upon the specific test case.

Typically, QPSK could be used for the modulation of the OCNGtransmission. However, depending upon the test also higher ordermodulation could be used. In a specific embodiment, the modulation usedfor resources allocated to the virtual users 604 is the same as used forthe one or more UEs 603 under test.

In case MIMO (multiple transmit and receive antennas, transmitdiversity, cyclic delay diversity, etc) is used, the OCNG can betransmitted from uncorrelated sources, i.e. uncorrelated transmitantennas. Alternatively depending upon the type of test the OCNG can usethe same MIMO transmission method and the same correlation model whichis used for data transmission to the test user.

FIG. 6 illustrates schematically a transmitting unit 600, which can be abase station such as an eNodeB in the case where the test is performedin a real network, or a test equipment such as a system simulator in thecase where the test is performed in a lab. For the sake of clarity, onlyunits that are relevant for this invention are illustrated in thisfigure. A processing unit 601 is configured to split the resources to beused for transmission into contiguous unities in the frequency domainaccording to a specific rule, and a transmitter 602 is configured totransmit to the UE 603 under test and to virtual users 604, alsoreferred to as OCNG users.

Thus, embodiments of the present invention provide the advantages that:

-   -   The load generation in a test is simplified and testing        complexity is reduced.    -   The load generation in a base station such as an e-NodeB is        simplified based on the rules above for load tests in real        networks.    -   Performance requirements can be properly verified since        consistent rules for generating load in the cell are used in the        tests since well defined load generation will allow easy        distinction between the performance of good and bad UEs.

An implementation of the invention is exemplified in the following,which constitutes an example of how embodiments of the invention couldbe included in TS 36.133 version 8.4.0:

OP.1 FDD: OCNG FDD Pattern 1 (outer resource blocks allocation) Relativepower level γ_(PRB) [dB] Subframe Alloca- 0 5 1-4, 6-9 tion Controlregion OFDM symbols^(Note 2) PDSCH n_(PRB) CP length 1 2 3 1 2 3 1 2 3Data  0-12 N 0 0 0 Note 1 37-49 N 0 0 0 Note 1: Each physical resourceblock (PRB) is assigned to an individual virtual UE. The data for eachvirtual UE shall be uncorrelated with data from other virtual UEs overthe period of any measurement. The data shall be QPSK modulated. Theparameter γ_(PRB) is used to scale the power of PDSCH. Note 2: Thecontrol region consists of PCFICH, PHICH and PDCCH. Number of OFDMsymbols belonging to the control region may vary between subframes. N:Normal

TABLE A.3.2.1.2-1 OP.2 FDD: OCNG FDD Pattern 2 (Full bandwidthallocation) Relative power level γ_(PRB) [dB] Subframe Alloca- 0 5 1-4,6-9 tion Control region OFDM symbols^(Note 2) PDSCH n_(PRB) CP length 12 3 1 2 3 1 2 3 Data 0-49 N 0 0 0 Note 1 Note 1: Each physical resourceblock (PRB) is assigned to an individual virtual UE. The data for eachvirtual UE shall be uncorrelated with data from other virtual UEs overthe period of any measurement. The data shall be QPSK modulated. Theparameter γ_(PRB) is used to scale the power of PDSCH. Note 2: Thecontrol region consists of PCFICH, PHICH and PDCCH. Number of OFDMsymbols belonging to the control region may vary between subframes. N:Normal

OP.1 TDD: OCNG TDD Pattern 1 (outer resource blocks allocation) for 5 msdownlink- to-uplink switch-point periodicity Relative power levelγ_(PRB) [dB] Subframe 0 5 3, 4, 8, 9^(Note 2) 1, 6 Allocation Controlregion OFDM symbols^(Note 3) PDSCH n_(PRB) CP length 1 2 3 1 2 3 1 2 3 12 Data  0-12 N 0 0 0 Table Note 1 37-49 N 0 0 0 A.3.2.2.1-2 Note 1: Eachphysical resource block (PRB) is assigned to an individual virtual UE.The data for each virtual UE shall be uncorrelated with data from othervirtual UEs over the period of any measurement. The data shall be QPSKmodulated. The parameter γ_(PRB) is used to scale the power of PDSCH.Note 2: Subframes available for DL transmission depends on theUplink-Downlink configuration defined in Table 4.2-2 in 3GPP TS 36.211[16]. Note 3: The control region consists of PCFICH, PHICH and PDCCH.Number of OFDM symbols belonging to the control region may vary betweensubframes. N: Normal

OP.1 TDD: OCNG TDD Pattern 1 ((outer resource blocks allocation) forspecial subframe configuration with 5 ms downlink-to-uplink switch-pointperiodicity Relative power level γ_(PRB) [dB] Special subframeconfiguration 0 1 2 3 4 5 6 7 8 Allocation Control region OFDM symbolsn_(PRB) CP length 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2  0-12 N 0 0 0 0 00 0 0 0 37-49 N 0 0 0 0 0 0 0 0 0 Note 1: Special subframeconfigurations are defined in Table 4.2-1 in TS 36.211 [16].

TABLE A.3.2.2.2-1 OP.2 TDD: OCNG TDD Pattern 2 (full bandwidthallocation) for 5 ms downlink-to-uplink switch-point periodicityRelative power level γ_(PRB) [dB] Subframe 0 5 3, 4, 8, 9^(Note 2) 1, 6Allocation Control region OFDM symbols^(Note 3) PDSCH n_(PRB) CP length1 2 3 1 2 3 1 2 3 1 2 Data 0-49 N 0 0 0 Table Note 1 A.3.2.2.2-2 Note 1:Each physical resource block (PRB) is assigned to an individual virtualUE. The data for each virtual UE shall be uncorrelated with data fromother virtual UEs over the period of any measurement. The data shall beQPSK modulated. The parameter γ_(PRB) is used to scale the power ofPDSCH. Note 2: Subframes available for DL transmission depends on theUplink-Downlink configuration in Table 4.2-2 in 3GPP TS 36.211 [16].Note 3: The control region consists of PCFICH, PHICH and PDCCH. Numberof OFDM symbols belonging to the control region may vary betweensubframes. N: Normal

OP.2 TDD: OCNG TDD Pattern 2 (full bandwidth allocation) for specialsubframe configuration with 5 ms downlink-to-uplink switch-pointperiodicity Relative power level γ_(PRB) [dB] Special subframeconfiguration 0 1 2 3 4 5 6 7 8 Allocation Control region OFDM symbolsn_(PRB) CP length 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 0-49 N 0 0 0 0 0 00 0 0 Note 1: Special subframe configurations are defined in Table 4.2-1in 3GPP TS 36.211 [16].

The abbreviations used in the specification have the following meanings:

-   OFDM: Orthogonal Frequency Division Multiplexing-   OFDMA: Orthogonal Frequency Division Multiple Access-   WCDMA: Wide band code division multiple access-   UE: User Equipment-   OCNS: Orthogonal channel noise simulator-   OCNG: OFMA channel noise generator-   SCH: Synchronisation Channel-   PBCH: Physical Broadcast Channel-   PCFICH: Physical Control Format Indicator Channel-   PDCCH: Physical Downlink Control Channel-   RB: Resource Block-   QPSK: Quadrature Phase Shift Keying

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive.

What is claimed is:
 1. A method for testing OFDM mobile terminals, saidmethod comprising: splitting radio resources available in a cell of anOFDM system into contiguous unities in the frequency domain, wherein oneor more of said unities comprises radio resources allocated to one ormore mobile terminals being tested and wherein at least one of saidunities comprises radio resources allocated to virtual users; andtransmitting test signals to said one or more mobile terminals on radioresources allocated to the mobile terminals and to the virtual users onradio resources allocated to said virtual users.
 2. The method accordingto claim 1 wherein splitting radio resources available in a cell of anOFDM system into contiguous unities in the frequency domain comprisessplitting the radio resources such that one or more contiguous unitiesof radio resources in the center of an available cell bandwidth areallocated to the one or more mobile terminals under test, and one ormore contiguous unities of radio resources at the edges of said cellbandwidth are allocated to virtual users.
 3. The method according toclaim 1 wherein splitting radio resources available in a cell of an OFDMsystem into contiguous unities in the frequency domain comprisessplitting the radio resources such that one or more contiguous unitiesof radio resources at the edges of said cell bandwidth are allocated tothe one or more mobile terminals under test, and one or more contiguousunities of radio resources in the center of an available cell bandwidthare allocated to virtual users.
 4. The method according to claim 1further comprising allocating one resource block out of the contiguousunities of radio resources available for the virtual users to each ofthe said virtual users.
 5. The method according to claim 1 whereintransmitting test signals to said virtual users on radio resourcesallocated to the virtual users comprises transmitting QPSK modulatedsignals to the virtual users on radio resources allocated to the virtualusers.
 6. The method according to claim 1 wherein transmitting testsignals to said virtual users on radio resources allocated to thevirtual users comprises transmitting test signals to the virtual usersfrom two or more uncorrelated transmit antennas.
 7. The method accordingto claim 1 wherein transmitting test signals to said virtual users onradio resources allocated to the virtual users comprises transmittingtest signals according to the same MIMO transmission method and usingsame correlation model as used for the one or more mobile terminalsunder test.
 8. The method according to claim 1 wherein the allocation ofradio resources to the one or more mobile terminals under test and thevirtual users respectively is fixed.
 9. The method according to claim 1wherein transmitting test signals to said one or more mobile terminalson radio resources allocated to the mobile terminals comprises the stepof transmitting PDSCH signals as test signals on radio resourcesallocated for the one or more mobile terminals.
 10. The method accordingto claim 1 carried out by an OFDMA simulator capable of simulating anOFDMA system.
 11. The method according to claim 1 carried out by a basestation capable of operating in an OFDMA system.
 12. A test apparatusfor testing mobile terminals in an OFDMA system, said test apparatuscomprising: a processing unit configured to split radio resources in anOFDMA cell into contiguous unities in the frequency domain, wherein oneor more of said unities comprise radio resources allocated to one ormore mobile terminals being tested and wherein at least one of saidunities comprise radio resources allocated to virtual users; and atransmitter operatively connected to said processing unit fortransmitting test signals to said one or more mobile terminals on radioresources allocated to the mobile terminals and to the virtual users onradio resources allocated to said virtual users.
 13. The test apparatusaccording to claim 12 wherein said processing unit is configured tosplit the radio resources such that one or more contiguous unities ofradio resources in the center of an available cell bandwidth areallocated to the one or more mobile terminals under test, and one ormore contiguous unities of radio resources at the edges of said cellbandwidth are allocated to virtual users.
 14. The test apparatusaccording to claim 12, wherein said processing unit is configured tosplit the radio resources such that one or more contiguous unities ofradio resources at the edges of said cell bandwidth are allocated to theone or more mobile terminals under test, and one or more contiguousunities of radio resources in the center of an available cell bandwidthare allocated to virtual users.
 15. The test apparatus according toclaim 12 wherein said processing unit is configured to allocate oneresource block out of the contiguous unities of radio resourcesavailable for the virtual users to each of the said virtual users. 16.The test apparatus according to claim 12 wherein said processing unit isconfigured to use QPSK modulation for test signals transmitted on radioresources allocated to the virtual users.
 17. The test apparatusaccording to claim 12 wherein the processing unit and transmitter areconfigured to transmit test signals to the virtual users via two or moreuncorrelated transmit antennas to simulate MIMO operations.
 18. The testapparatus according to claim 12 wherein the processing unit andtransmitter are configured to transmit test signals to the virtual usersusing the same MIMO transmission method and the same correlation modelas used for the one or more mobile terminals under test to simulate MIMOoperations.
 19. The test apparatus according to claim 12 wherein theprocessing unit is configured to allocate radio resources to the one ormore mobile terminals under test and the virtual users in a fixedmanner.
 20. The test apparatus according to claim 12 wherein theprocessing unit and transmitter are configured to transmit PDSCH signalsas test signals on radio resources allocated to the one or more mobileterminals under test.
 21. The test apparatus according to claim 12wherein said test apparatus comprises an OFDMA simulator capable ofsimulating an OFDMA system.
 22. The test apparatus according to claim 12wherein said test apparatus comprises a base station capable ofoperating in an OFDMA system.